This invention relates to joining a plurality of discrete solid lead parts together so as to form a substantially metallurgically homogeneous joint having a predetermined shape. More specifically, this invention relates to forming a substantially metallurgically homogeneous battery element terminal post from the distal ends of a plurality of Pb-acid storage battery plate lugs.
Lead-acid storage batteries comprise essentially a container divided into a plurality of compartments each of which contains an electrochemically active cell element immersed in H.sub.2 SO.sub.4. The cell elements comprise a stack of alternating positive and negative polarity plates separated one from the other by a thin, microporous sheet known as a separator. Each of these plates typically comprises a leady active material pasted onto a reticulated lead, or lead alloy, structure called a grid. The grid supports the active material relative to the other plates in the element and conducts electrical current throughout the plate. In most commercial batteries the grids each have a lug projecting therefrom which serves to join the plate to other plates of like polarity within the cell element (e.g. all positive polarity plates) via a lead bar known as a plate strap. The plate strap usually includes a post, or the like, projecting therefrom for connecting the element to a terminal of the battery or to another plate strap post in an adjacent cell compartment. In either case the plate strap post typically passes through an aperture in the container or its cover and is sealed in the aperture to prevent leakage of H.sub.2 SO.sub.4 out of the compartment.
The lead required for the plate strap adds considerable weight to the battery and the extra steps required to manufacture and assemble the straps add to the production costs of the battery. Attempts have been made to eliminate the heavy and costly plate straps and to simply bundle the plate lugs together into a cell element terminal post which functions like the plate strap post. Ruetschi et al U.S. Pat. No. 2,883,443, for example, bundles the plate lugs together to form a joint and mechanically presses the joint to deform it into a cylindrical post for joining directly to a battery terminal. Such mechanically formed joints tend to have oxides and impurities at the interfaces between adjacent lugs which increase the electrical resistance of the joint, are oft times very difficult to seal in their apertures owing to the generally poor exterior conformation and surface resulting from cold forming alone and can delaminate or separate if poorly handled. Finally the cracks remaining between the lugs can wick electrolyte up into the post to the general detriment of the battery.
It is the principal object of the present invention to provide a process for vibratorily joining and shaping the distal ends of the several plate lugs of a Pb-acid storage battery element into a substantially metallurgically homogeneous joint or post for connecting the element to the battery's other electrochemical elements or its terminals.
It is another object of the present invention to provide a process for joining a variety of discrete, solid lead parts and shaping the joint formed therebetween.
These and other objects and advantages of the present invention will be more readily apparent from the detailed description thereof which follows.